Section 21 (4)(A) with LHA Tenant

Possession - Section 8 and Section 21

I need to give notice on a property in order to sell, but am not quite sure which date to specify as the last day of a period of the tenancy.

The tenancy is now periodic and began with rent payable calendar monthly in advance on 1 October 2007. I therefore believe that the next date for a Section 21 notice would therefore be 30 April 2010 as long as that arrived with the tenant by 28 February 2010.

The possible complicating factor is that since November 2008 the remaining tenant (there were two) has been receiving LHA which is paid to me direct every fortnight because the tenant seems unable to open a bank account.

If she did receive LHA herself, then I would still receive the rental from her monthly so I assume the fact that I am paid fortnightly does not alter the period of the tenancy and I should still quote the last day of the appropriate calendar month.

Am I right? If not can you please advise how to date the notice correctly.

Incidentally, the disposal is nothing to do with the tenant's behaviour. She has taken good care of the property and never given cause for complaint

Thank you.